Plasma processing apparatus and plasma processing method

ABSTRACT

A plasma processing apparatus includes a plasma-generation high-frequency power supply which generates plasma in a processing chamber, a biasing high-frequency power supply which applies high-frequency bias electric power to an electrode on which a sample is placed, a monitor which monitors a peak-to-peak value of the high-frequency bias electric power applied to the electrode, an electrostatic chuck power supply which makes the electrode electrostatically attract the sample, a self-bias voltage calculating unit which calculates self-bias voltage of the sample by monitoring the peak-to-peak value of the high-frequency bias electric power applied to the electrode, and an output voltage control unit which controls output voltage of the electrostatic chuck power supply based on the calculated self-bias voltage.

BACKGROUND OF THE INVENTION

The present invention relates to a plasma processing method and a plasmaprocessing apparatus (e.g. plasma etching apparatus) having a mechanismfor holding a sample or wafer (semiconductor wafer, liquid crystalsubstrate, etc.) on an electrode (sample stage) by means of theso-called electrostatic chuck (electrostatic attraction), and inparticular, to a plasma processing method and a plasma processingapparatus suitable for reducing damage to the inner wall of theprocessing chamber of the plasma processing apparatus caused by a risein plasma potential.

In a plasma processing apparatus such as a plasma etching apparatus, amethod called “electrostatic chuck” or “electrostatic attraction” iswidely used for holding a wafer in the processing chamber. Theelectrostatic chuck (electrostatic attraction) is a method of holding awafer on an electrode (sample stage) by electrostatic force which iscaused by the potential difference between the wafer and the electrode.The electrostatic chuck has advantages over mechanical holding methods(using a holding member such as a clamp) in that wafer contamination dueto contact can be avoided and wafer temperature control is easy (sincethe whole of the back of the wafer is attracted). Methods for theelectrostatic chuck generally include a monopole method (applyingelectrostatic chuck voltage to one electrode) and a dipole method (usingtwo or more electrodes and generally applying electrostatic chuckvoltages of different polarities to the electrodes, respectively).

FIG. 2 is a schematic diagram showing the general composition of aplasma processing apparatus.

An electrostatic chuck power supply 111 is capable of applying DCvoltage to an electrode 108 which is embedded in a sample stage 109. Thevalue of the DC voltage will hereinafter be referred to as “ESC voltage(output voltage) of the electrostatic chuck power supply 111”. Averageelectric potential of the wafer 113 caused by application of output of abiasing high-frequency power supply 110 to the electrode 108 via acapacitor will hereinafter be referred to as “self-bias voltage”(V_(dc)). The self-bias voltage V_(dc) is a negative DC voltage. In thiscase, the potential difference between the electrode 108 and the wafer113 (i.e. the difference between the ESC voltage and the self-biasvoltage V_(dc)) is the electrostatic chuck voltage (V_(chuck)). Theself-bias voltage V_(dc) is dependent on the peak-to-peak value (V_(pp))of the high-frequency bias power applied to the wafer 113 in thefollowing relationship:α=|V _(dc) /V _(pp)|≦0.5where α is a constant which can vary depending on the plasma processingapparatus (0.3-0.45 in a standard plasma processing apparatus).

The peak-to-peak value V_(pp) can be monitored with a V_(pp) monitor112.

FIG. 3 is a graph showing an example of the relationship among the ESCvoltage, the self-bias voltage V_(dc), the peak-to-peak value V_(pp) andthe electrostatic chuck voltage V_(chuck).

The self-bias voltage V_(dc) appears in the negative region of the graphwith an absolute value α×V_(pp) (positive). As shown in FIG. 3, thereexist two ESC voltages that cause the same V_(chuck) with respect to thevalue of V_(dc). The ESC voltages on the positive side and on thenegative side of V_(dc) will hereinafter be expressed as V_(ESC) ⁺ andV_(ESC) ⁻, respectively.

In this case, the relationship among the ESC voltages (V_(ESC) ⁺,V_(ESC) ⁻), the electrostatic chuck voltage V_(chuck) and the self-biasvoltage V_(dc) can be expressed by the following equations:V _(ESC) ⁺ =V _(dc) +V _(chuck)V _(ESC) ⁻ =V _(dc) −V _(chuck)where V_(dc) is negative and V_(chuck) is positive.

SUMMARY OF THE INVENTION

The existing plasma processing apparatuses (related arts) involve thefollowing problems regarding the holding of the wafer by means ofelectrostatic chuck (electrostatic attraction).

First, when the electrostatic chuck voltage V_(chuck) is too low, thewafer, not sufficiently attracted to the electrode, can peel off fromthe electrode (sample stage) during the plasma processing. On the otherhand, when the electrostatic chuck voltage V_(chuck) is too high, chuckforce (attracting force) becomes too high and the wafer can be cracked.Therefore, the peeling off and cracking of the wafer have to beprevented by properly adjusting the value of the electrostatic chuckvoltage V_(chuck).

Further, when resistance at the inner wall of the processing chambermaking contact with the plasma is high, abnormal electric dischargeoccurs between the plasma and the inner wall.

For example, when plasma 106 for the processing of the wafer 113 isgenerated by applying positive ESC voltage to the electrode 108 by themonopole method, minute leak current I (indicated with a broken line inFIG. 2) flows into the plasma. When the resistance R of the inner wallof the processing chamber 105 is high, the plasma is electricallycharged up to a voltage V=IR (positive), that is, the plasma potentialtakes on a positive value. When the plasma potential exceeds a certainlevel, abnormal electric discharge occurs due to electric breakdown ofan insulator layer on the inner wall of the processing chamber. Due toforeign materials caused by the abnormal electric discharge,contamination of the wafer and the inside of the processing chamberbecomes a problem.

In order to suppress the abnormal electric discharge and theaccompanying generation of foreign materials, various techniques forsuppressing the rise in the plasma potential (the cause of the abnormalelectric discharge) have been proposed.

For example, in a technique described in JP-A-2007-73309, the potentialof the wall is measured and the absolute value of the ESC voltage isreduced when abnormal electric discharge is likely to occur.

However, this technique involves problems such as the peeling off of thewafer due to the reduced absolute value of the ESC voltage, unevennessof the plasma processing due to nonuniformity in wafer temperature(caused by changes in the chuck force during the process due to thechanging (adjustment) of the ESC voltage during the process), etc.

Meanwhile, a technique described in JP-A-2006-210726 suppresses the risein the plasma potential by negatively shifting the ESC voltage.

With this technique, however, the voltage applied to the electrodebecomes extremely high especially when V_(pp) and V_(dc) are both high,which is undesirable in consideration of dielectric strength of aflame-sprayed film of the electrode head and the transmission system,costs, etc.

It is therefore the primary object of the present invention to provide aplasma processing apparatus and a plasma processing method capable ofresolving the above problems, such as the wafer peeling (peeling off ofthe wafer) caused by insufficient chuck force, the wafer cracking(cracking of the wafer) caused by excessive chuck force, the unevennessof plasma processing, the abnormal electric discharge (due to the risein the plasma potential) and the accompanying generation of foreignmaterials, power loss caused by excessive supply voltage, and theproblem related to dielectric strength and costs.

In accordance with an aspect of the present invention, there is provideda plasma processing apparatus including a plasma-generationhigh-frequency power supply which generates plasma in a processingchamber, a biasing high-frequency power supply which applieshigh-frequency bias electric power to an electrode on which a sample isplaced, a monitor which monitors a peak-to-peak value of thehigh-frequency bias electric power applied to the electrode, anelectrostatic chuck power supply which makes the electrodeelectrostatically attract the sample, a self-bias voltage calculatingunit which calculates self-bias voltage of the sample by monitoring thepeak-to-peak value of the high-frequency bias electric power applied tothe electrode, and an output voltage control unit which controls outputvoltage of the electrostatic chuck power supply based on the calculatedself-bias voltage.

Preferably, when the absolute value of the self-bias voltage is smallerthan electrostatic chuck voltage necessary for the attraction of thesample, the output voltage control unit sets the output voltage at(self-bias voltage)−(electrostatic chuck voltage).

Preferably, when the absolute value of the self-bias voltage is largerthan electrostatic chuck voltage necessary for the attraction of thesample, the output voltage control unit sets the output voltage at(self-bias voltage)+(electrostatic chuck voltage).

Preferably, when the obtained output voltage is smaller than aprescribed value, the output voltage control unit sets the outputvoltage at a value which is on the negative side of the self-biasvoltage and capable of achieving the electrostatic chuck voltagenecessary for the attraction of the sample only at plasma ignition.

Preferably, the plasma processing apparatus further includes a controlunit which stops supply of gas to the back of the sample whileprocessing of the sample shifts from a step to the next step in caseswhere the processing of the sample includes multiple steps which areexecuted successively and electrostatic chuck voltage varies from stepto step.

In accordance with another aspect of the present invention, there isprovided a plasma processing method using a plasma processing apparatusequipped with a plasma-generation high-frequency power supply whichgenerates plasma in a processing chamber, a biasing high-frequency powersupply which applies high-frequency bias electric power to an electrodeon which a sample is placed, a monitor which monitors a peak-to-peakvalue of the high-frequency bias electric power applied to theelectrode, and an electrostatic chuck power supply which makes theelectrode electrostatically attract the sample. In the plasma processingmethod, the electrostatic chuck of the sample is carried out by settingoutput voltage of the electrostatic chuck power supply at a negativevalue which is on the positive side of self-bias voltage of the sample.

In accordance with another aspect of the present invention, there isprovided a plasma processing method using a plasma processing apparatusequipped with a plasma-generation high-frequency power supply whichgenerates plasma in a processing chamber, a biasing high-frequency powersupply which applies high-frequency bias electric power to an electrodeon which a sample is placed, a monitor which monitors a peak-to-peakvalue of the high-frequency bias electric power applied to theelectrode, and an electrostatic chuck power supply which makes theelectrode electrostatically attract the sample. In the plasma processingmethod, the electrostatic chuck of the sample is carried out by settingoutput voltage of the electrostatic chuck power supply at a negativevalue which is on the negative side of self-bias voltage of the sampleat plasma ignition and thereafter setting the output voltage at anegative value which is on the positive side of the self-bias voltage ofthe sample.

Preferably, supply of gas to the back of the sample is stopped whileprocessing of the sample shifts from a step to the next step in caseswhere the processing of the sample includes multiple steps which areexecuted successively and electrostatic chuck voltage varies from stepto step.

With the plasma processing apparatus and the plasma processing method inaccordance with the present invention, appropriate electrostatic chuckforce can be achieved under a condition avoiding the problems with theconventional techniques (abnormal electric discharge due to a rise inthe plasma potential and the accompanying generation of foreignmaterials, the problem related to the dielectric strength of theelectrode substrate and the transmission system caused by theapplication of high voltage).

Further, stable electrostatic chuck force can be achieved withoutwasting electric power since the wafer can be attracted to the electrodeby use of low applied voltage within a permissible range.

Incidentally, while inductively coupled plasma is used as an example inthe plasma processing apparatus in the following embodiments, thepresent invention achieves the same effects even when a generally-usedplasma generating unit of a different type (magneto-microwave plasma,etc.) is used.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart showing a method which is used for determining ESCvoltage in embodiments in accordance with the present invention.

FIG. 2 is a schematic diagram showing the general composition of aplasma processing apparatus.

FIG. 3 is a graph showing an example of the relationship among ESCvoltage, self-bias voltage V_(dc), a peak-to-peak value V_(pp) andelectrostatic chuck voltage V_(chuck).

FIG. 4 is a graph showing an example of the relationship between plasmapotential and the ESC voltage in a case where the absolute value of theself-bias voltage V_(dc) is smaller than the electrostatic chuck voltageV_(chuck).

FIG. 5 is a graph showing an example of the relationship between theplasma potential and the ESC voltage in a case where the absolute valueof the self-bias voltage V_(dc) is larger than the electrostatic chuckvoltage V_(chuck).

FIG. 6 is a graph showing still another example of the relationshipbetween the plasma potential and the ESC voltage in a case where V_(ESC)⁺ is negative, |V_(ESC) ⁺|<β and additional voltage is added to the ESCvoltage only at plasma ignition.

FIG. 7 is a graph showing an example of the relationship among the ESCvoltage, the self-bias voltage V_(dc), the peak-to-peak value V_(pp),the electrostatic chuck voltage V_(chuck) and gas pressure on the backof the wafer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, a description will be given in detail ofpreferred embodiments in accordance with the present invention.

In order to resolve the problems with the related art, the presentinventors conducted various experiments for studying the relationshipbetween the plasma potential and the ESC voltage (DC voltage outputtedby the electrostatic chuck power supply 111 to be applied to theelectrode 108).

FIG. 4 is a graph showing an example of the relationship between theplasma potential and the ESC voltage in a case where the absolute valueof the self-bias voltage V_(dc) is smaller than the electrostatic chuckvoltage V_(chuck).

In FIG. 4, V_(plasma) ⁺ represents the plasma potential when V_(ESC) ⁺(ESC voltage on the positive side of V_(dc)) is used, and V_(plasma) ⁻represents the plasma potential when V_(ESC) ⁻ (ESC voltage on thenegative side of V_(dc)) is used. Under the condition shown in FIG. 4,V_(ESC) ⁺ is positive and V_(ESC) ⁻ is negative.

In this case, a rise in the plasma potential was observed when thepositive ESC voltage V_(ESC) ⁺ was used, and it was found that abnormalelectric discharge occurs when the plasma potential gets high in thepositive region.

Thus, in order to prevent the abnormal electric discharge, the ESCvoltage employed has to be changed depending on the behavior of theplasma potential.

In the following, the setting of ESC voltage that is capable ofachieving appropriate electrostatic chuck force without causing theabnormal electric discharge (occurring dependent on each value ofV_(ESC) ⁺) will be explained with reference to FIGS. 4, 5 and 6.

First, a value of the electrostatic chuck voltage V_(chuck) that can beregarded as optimum is set. The electrostatic chuck voltage V_(chuck)should be set at a value that causes no wafer peeling (peeling off ofthe wafer) or wafer cracking (cracking of the wafer). The electrostaticchuck voltage “V_(chuck)” in the following explanation means this value(a constant which is set here).

Subsequently, the peak-to-peak value V_(pp) of the high-frequency biaselectric power applied to the electrode 108 is monitored and the valueof the self-bias voltage V_(dc) is calculated from the monitoredpeak-to-peak value V_(pp) and the preset coefficient α(α=|V_(dc)/V_(pp)|≦0.5).

In order to realize the electrostatic chuck (electrostatic attraction)of the wafer 113 by use of V_(chuck) (set value) with respect to thecalculated V_(dc), it is necessary to select which of V_(ESC) ⁺ orV_(ESC) ⁻ should be used.

The absolute value of V_(ESC) ⁺ is constantly smaller than that ofV_(ESC) ⁻ since V_(dc) is negative. Thus, necessary electric power canbe reduced by using V_(ESC) ⁺ instead of using V_(ESC) ⁻. However, theplasma potential V_(plasma) ⁺ becomes positive when V_(ESC) ⁺ ispositive as shown in FIG. 4, which involves a possibility of abnormalelectric discharge.

On the other hand, the plasma potential V_(plasma) ⁻ is constantlynegative since V_(ESC) ⁻ is constantly negative. Thus, the use ofV_(ESC) ⁻ involves no danger of abnormal electric discharge.

Based on the above consideration, V_(ESC) ⁻ is used in the followingembodiments when V_(ESC) ⁺ is positive (i.e. when |V_(dc)|<V_(chuck)).

FIG. 5 is a graph showing an example of the relationship between theplasma potential and the ESC voltage in a case where the absolute valueof the self-bias voltage V_(dc) is larger than the electrostatic chuckvoltage V_(chuck).

In this case where V_(ESC) ⁺ is negative (i.e. |V_(dc)|>V_(chuck)),V_(ESC) ⁺ and V_(ESC) ⁻ are both negative, which involves no danger ofabnormal electric discharge irrespective of whether V_(ESC) ⁺ or V_(ESC)⁻ is used. Therefore, the use of V_(ESC) ⁺ (having a smaller absolutevalue than V_(ESC) ⁻) is suitable for realizing smaller output voltageand is advantageous in consideration of the dielectric strength of theelectrode substrate and the transmission system, electric powerconsumption, etc.

In the case where V_(ESC) ⁺ is negative, however, an experiment showedthat the plasma potential behaves in two ways (having a positivehigh-voltage peak or no peak when the plasma is ignited) depending onthe absolute value of the employed V_(ESC) ⁺.

In the example shown in FIG. 5, the plasma potential V_(plasma) ⁺ showsa positive high-voltage peak at the plasma ignition and thereafterremains at a negative level (stationary state).

It was found that the positive high-voltage peak at the plasma ignitionappears when |V_(ESC) ⁺| is small and disappears when |V_(ESC) ⁺| isincreased (with V_(ESC) ⁺ in the negative region). From this result, itcan be considered that there exist a threshold value of V_(ESC) ⁺(hereinafter referred to as “β”) for eliminating the positivehigh-voltage peak at the plasma ignition. It was also found that thethreshold value β can be estimated by previously conducting anexperiment.

Therefore, when the plasma potential V_(plasma) ⁺ has no positivehigh-voltage peak at the plasma ignition (i.e. when |V_(ESC) ⁺|>β), theplasma potential smoothly shifts to the negative region since the plasmaignition and thereafter remains negative, with no problem occurring withthe use of V_(ESC) ⁺. Thus, V_(ESC) ⁺ is used in this case.

On the other hand, when the plasma potential V_(plasma) ⁺ has a positivehigh-voltage peak at the plasma ignition (i.e. when |V_(ESC) ⁺|<β),there is a possibility of the aforementioned abnormal electric discharge(even if the positive high-voltage peak appears only at the plasmaignition), which is problematic.

Thus, in order to resolve the problem of the positive high plasmapotential at the plasma ignition, an additional voltage, for increasingthe absolute value of the ESC voltage (V_(ESC) ⁺) within the negativeregion, is added to the ESC voltage at the plasma ignition in thefollowing embodiments.

FIG. 6 is a graph showing an example of the relationship between theplasma potential and the ESC voltage in the case where V_(ESC) ⁺ isnegative, |V_(ESC) ⁺<β and the additional voltage (for increasing theabsolute value of the ESC voltage (V_(ESC) ⁺) within the negativeregion) is added to the ESC voltage only at the plasma ignition.

Thanks to the additional voltage for increasing the absolute value ofV_(ESC) ⁺ within the negative region, the positive high plasma potentialpeak at the plasma ignition (which was seen in FIG. 5) was suppressedsuccessfully and the plasma potential remained constantly in thenegative region. Thus, there is no possibility of abnormal electricdischarge in this case. A (negative) voltage of approximately V_(ESC) ⁻or lower can be considered to be sufficient for the additional voltageused at the plasma ignition.

FIG. 1 is a chart showing a method which is used for determining the ESCvoltage in the following embodiments.

First, the value of the electrostatic chuck voltage V_(chuck) is set andthe self-bias voltage V_(dc) is calculated from the monitoredpeak-to-peak value V_(pp) and the coefficient α predeterminedexperimentally or theoretically.

Subsequently, whether V_(ESC) ⁺ is positive or not (i.e. whether|V_(dc)|<V_(chuck) or not) is judged.

When V_(ESC) ⁺ is positive (i.e. |V_(dc)|<V_(chuck)), V_(ESC) ⁻ is usedas the ESC voltage. When V_(ESC) ⁺ is negative (i.e.|V_(dc)|>V_(chuck)), V_(ESC) ⁺ is used as the ESC voltage.

In the case where V_(ESC) ⁺ is used as the ESC voltage, if |V_(ESC)⁺|<β, the additional voltage (for increasing the absolute value of theESC voltage within the negative region) is added to the ESC voltageV_(ESC) ⁺ at the plasma ignition and thereafter the ESC voltage is setat V_(ESC) ⁺. If |V_(ESC) ⁺|>β, the ESC voltage is set constantly atV_(ESC) ⁺ from the plasma ignition. Incidentally, β is a preset positiveconstant.

By determining the ESC voltage according to the above chart, it ispossible to provide a plasma processing apparatus and a plasmaprocessing method capable of achieving appropriate electrostatic chuckforce without causing abnormal electric discharge.

Embodiment 1

A plasma processing apparatus and a plasma processing method inaccordance with a first embodiment of the present invention will bedescribed below with reference to FIGS. 1 and 2.

Referring to FIG. 2, the plasma processing apparatus of this embodimentincludes a plasma-generation high-frequency power supply 101 forgenerating plasma in a processing chamber 105, a biasing high-frequencypower supply 110 for applying high-frequency bias electric power to anelectrode 108 on which a wafer 113 is placed, a V_(pp) monitor 112 formonitoring the peak-to-peak value V_(pp) of the high-frequency biaselectric power applied to the electrode 108, an electrostatic chuckpower supply 111 for making the electrode 108 (sample stage 109)electrostatically attract the wafer 113, a self-bias voltage calculatingunit 114 for calculating the self-bias voltage V_(dc) of the wafer 113by monitoring the peak-to-peak value V_(pp) of the high-frequency biaselectric power applied to the electrode 108, and an output voltagecontrol unit 115 for controlling the output voltage of the electrostaticchuck power supply 111 (ESC voltage) based on the calculated self-biasvoltage V_(dc). The wafer 113 held on the electrode 108 (sample stage109) by the electrostatic chuck force is treated with plasma (plasmatreatment). In the figure, a reference numeral 103 depicts an antenna,104 an inductive coupling window and 107 a ground electrode.

The value of the output voltage of the electrostatic chuck power supply111 (ESC voltage) is determined by use of the monitored peak-to-peakvalue V_(pp), the electrostatic chuck voltage V_(chuck) which haspreviously been set, and the coefficients α and β which have previouslybeen measured or set.

A case where V_(chuck)=300 V, α=0.4 and β=200 V will be described belowas an example.

When the measured peak-to-peak value V_(pp) is 300 V, the self-biasvoltage calculating unit 114 calculates the self-bias voltage V_(dc) as−120 V. Since |V_(dc)|<V_(chuck) (i.e. V_(ESC) ⁺>0) holds, the outputvoltage control unit 115 sets the ESC voltage at V_(ESC)⁻=V_(dc)−V_(chuck)=−420 V.

When the measured peak-to-peak value V_(pp) is 1000 V, the self-biasvoltage calculating unit 114 calculates the self-bias voltage V_(dc) as−400 V. Since |V_(dc)|>V_(chuck) (i.e. V_(ESC) ⁺<0) holds, the outputvoltage control unit 115 uses V_(ESC) ⁺ (=V_(dc)+V_(chuck)=−100 V) asthe ESC voltage. In this case, |V_(ESC) ⁺|<β holds (since V_(ESC) ⁺=−100V and β=200 V), and thus the output voltage control unit 115 executesthe control to add the additional voltage (approximately V_(ESC)⁻=V_(dc)−V_(chuck)=−700 V) to the ESC voltage V_(ESC) ⁺only at theplasma ignition.

When the measured peak-to-peak value V_(pp) is 2000 V, the self-biasvoltage calculating unit 114 calculates the self-bias voltage V_(dc) as−800 V. Since |V_(dc)|>V_(chuck) (i.e. V_(ESC) ⁺<0) holds, the outputvoltage control unit 115 uses V_(ESC) ⁺(=V_(dc)+V_(chuck)=−500 V) as theESC voltage. In this case, the additional voltage at the plasma ignitionis unnecessary since |V_(ESC) ⁺|>β holds (since V_(ESC) ⁺=−500 V andβ=200 V), and thus the output voltage control unit 115 sets the outputvoltage (ESC voltage) at V_(ESC) ⁺=−500 V from the plasma ignition.

By controlling the ESC voltage as in the above examples, theelectrostatic chuck voltage is maintained constantly at the set valueV_(chuck), by which the wafer peeling and the wafer cracking areavoided. Further, the abnormal electric discharge is eliminated sincethe aforementioned rise in the plasma potential due to positive leakcurrent is prevented.

Embodiment 2

A plasma processing apparatus and a plasma processing method inaccordance with a second embodiment of the present invention will bedescribed below with reference to FIG. 7.

In this embodiment, a case where the processing of the wafer includesmultiple steps which are executed successively and the peak-to-peakvalue V_(pp) (of the high-frequency bias electric power applied to theelectrode 108) varies from step to step will be described.

FIG. 7 is a graph showing an example of the relationship among the ESCvoltage, the self-bias voltage V_(dc), the peak-to-peak value V_(pp),the electrostatic chuck voltage and gas pressure on the back of thewafer.

In the case where multiple steps differing in the peak-to-peak valueV_(pp) are executed successively, the electrostatic chuck (electrostaticattraction) of the wafer has to be carried out in each step by use of anESC voltage suitable for the peak-to-peak value V_(pp) in the step, thatis, an ESC voltage capable of achieving appropriate electrostatic chuckforce without causing the abnormal electric discharge.

In this case, a problem can occur when the employed ESC voltage ischanged from V_(ESC) ⁺ to V_(ESC) ⁻ or from V_(ESC) ⁻ to V_(ESC) ⁺ inthe transition between two consecutive steps.

For example, a case where V_(chuck)=300 V, α=0.4 and β=200 V (theaforementioned condition) will be considered below.

When two successive steps in which the peak-to-peak value V_(pp) changesfrom 300 V to 1000 V are executed, the self-bias voltage V_(dc) changesfrom −120 V to −400 V. According to the chart of FIG. 1, the ESC voltagechanges continuously from −420 V to −100 V in this case. Since theplasma changes continuously, no positive high plasma potential (likethat appearing at the plasma ignition) occurs in the transition betweenthe two steps. Thus, in the process in which the ESC voltage changes,there is a point in time when the ESC voltage becomes equal to V_(dc) orthe difference between V_(dc) and the ESC voltage becomes smaller thanV_(chuck). At this point, the electrostatic chuck (electrostaticattraction) of the wafer becomes insufficient, and in the plasmaprocessing apparatus in which gas (e.g. He) is supplied to the back ofthe wafer (for the purpose of temperature control, chuck forcemeasurement, etc.), trouble such as wafer peeling or wafer flying can becaused by the pressure of the gas (e.g. He).

In this embodiment which is designed to resolve the above problem, whenthe employed ESC voltage is changed from V_(ESC) ⁺ to V_(ESC) ⁻ or fromV_(ESC) ⁻ to V_(ESC) ⁺ in the transition between steps, a control unit116 (unshown) stops the supply of the gas (e.g. He) to the back of thewafer (a step of removing the gas on the back of the wafer) before thetransition as shown in FIG. 7.

By the above step, the gas on the back of the wafer is removed when theESC voltage is changed. Consequently, the ESC voltage can be changedsafely without the danger of wafer peeling, wafer flying, etc.

It should be further understood by those skilled in the art thatalthough the foregoing description has been on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A plasma processing method of involving electrostatic chucking asample in a plasma processing apparatus equipped with aplasma-generation high-frequency power supply which generates plasma ina processing chamber, a biasing high-frequency power supply whichapplies high-frequency bias electric power to an electrode on which thesample is placed, a monitor which monitors a peak-to-peak value of thehigh-frequency bias electric power applied to the electrode, and anelectrostatic chuck power supply which makes the electrodeelectrostatically attract the sample, the method comprising steps of:setting an output voltage of the electrostatic chuck power supply at afirst negative value during a predetermined period after plasma ignitionuntil plasma potential becomes stable; determining a second negativevalue for the output voltage of the electrostatic chuck power supplybased upon an output from the monitor, the determined second negativevalue being greater than a self-bias voltage of the sample and greaterthan the first negative value; and after setting the output voltage atthe first negative value during the predetermined period after theplasma ignition until the plasma potential becomes stable, setting theoutput voltage at the determined second negative value for plasmaprocessing of the sample.
 2. The method according to claim 1, whereinthe first negative value of the output voltage of the electrostaticchuck power supply is set, during the predetermined period after theplasma ignition, to be less than the plasma potential.